Electronic pen

ABSTRACT

An electronic pen includes a coil wound around a magnetic core, a first capacitor forming a resonance circuit with the coil, a rectifier circuit which, in operation, rectifies an alternating-current signal received by the resonance circuit, the rectifier circuit including a second capacitor, a voltage detecting circuit which, in operation, detects whether a rectified output voltage across the second capacitor of the rectifier circuit exceeds a predetermined value, a third capacitor having a capacitance that is larger than a capacitance of the second capacitor, and a charge control circuit which, in operation, controls supply of a charging current to the third capacitor by the rectified output voltage. The charge control circuit in operation, causes the charging current to be fed to the third capacitor by the rectified output voltage when the voltage detection circuit detects that the rectified output voltage obtained across the second capacitor exceeds the predetermined value.

BACKGROUND Technical Field

The present disclosure relates to an electronic pen of anelectromagnetic induction type.

Description of Related Art

As an input device for a personal computer or the like, a positiondetecting device is known which has an input surface for performingpointing operation and input of characters, figures, and the like andwhich detects a position indicated by an electronic pen on the inputsurface by an electromagnetic induction system. As the electromagneticinduction type electronic pen used for the position detecting device, anelectronic pen is known which receives an electromagnetic wave from theposition detecting device by a resonance circuit constituted of a coiland a capacitor, and which feeds back the received electromagnetic waveto the position detecting device, so that the position detecting devicedetects a position indicated by the electronic pen (see, for example,Patent Document 1 (Japanese Patent Laid-Open No. 2004-212973)).

The electromagnetic induction type electronic pen of this kind has afeature of being able to send and receive the electromagnetic wave toand from the position detecting device through the resonance circuitthat does not need a cell (battery) power supply. There is anotherfeature in that even in a case where the electronic pen of this kindincludes an electronic circuit that needs power supply, necessary powercan be obtained by rectifying the electromagnetic wave received from theposition detecting device through the resonance circuit (see, forexample, Patent Document 2 (Japanese Patent No. 5892595)).

FIG. 7 is a diagram showing an example of configuration of an electroniccircuit of a conventional electronic pen of this kind. As shown in FIG.7, in the electronic pen in the present example, a parallel resonancecircuit 3 is formed by connecting a resonance capacitor 2 in parallelwith a coil 1 wound around a magnetic core disposed on a pen tip side.

One terminal of the parallel resonance circuit 3 is grounded, andanother terminal of the parallel resonance circuit 3 is connected to arectifier circuit 5 via a capacitor 4. The rectifier circuit 5 includestwo diodes 6 and 7 and a capacitor 8 that stores a rectified outputvoltage. The rectified output voltage obtained across the capacitor 8 inthe rectifier circuit 5 is supplied to a voltage stabilizing circuit 9,stabilized by the voltage stabilizing circuit 9, and then supplied as apower supply voltage for a pen control circuit 10 constituted of an IC(Integrated Circuit), for example.

The pen control circuit 10, for example, performs control fortransmitting a predetermined signal to a position detecting device bycontrolling a signal fed back to the position detecting device throughthe parallel resonance circuit 3. Specifically, in the example of FIG.7, a switch circuit 11 is connected in parallel with the coil 1 and thecapacitor 2 of the parallel resonance circuit 3. The switch circuit 11is turned on and off by a switching control signal from the pen controlcircuit 10 to control resonant operation of the parallel resonancecircuit 3. When the switch circuit 11 is off, the parallel resonancecircuit 3 performs the resonant operation. When the switch circuit 11 ison, the parallel resonance circuit 3 stops the resonant operationbecause a short circuit occurs across the capacitor 2.

The pen control circuit 10 generates a binary digital signal asinformation to be transmitted to the position detecting device, andsupplies the binary digital signal as the switching control signal tothe switch circuit 11. The switch circuit 11 is, for example, turned offwhen the binary digital signal is “1” and is turned on when the binarydigital signal is “0.” The resonant operation of the parallel resonancecircuit 3 is thereby controlled.

The signal from the position detecting device is fed back to theposition detecting device when the parallel resonance circuit 3 performsthe resonant operation, but is not fed back to the position detectingdevice when the parallel resonance circuit 3 stops the resonantoperation. Thus, the digital signal from the electronic pen istransmitted as an ASK (Amplitude Shift Keying) signal or an OOK (On OffKeying) signal to the position detecting device. The position detectingdevice detects the digital signal transmitted from the electronic pen byreconstructing the digital signal from the ASK signal or the OOK signalreceived from the electronic pen.

For highly responsive operation of the electronic pen at a time ofbringing the electronic pen near the position detecting device, thestorage capacitor 8 in the rectifier circuit 5 preferably has arelatively small capacitance to quickly provide the power supply voltageto be supplied to the pen control circuit 10. However, in a case wherethe capacitor 8 in the rectifier circuit 5 has a small capacitance, whenthe electronic pen is once moved away from the position detectingdevice, power supplied from the position detecting device is decreased,and consequently a voltage stored in the capacitor 8 falls sharply. Evenwhen the electronic pen is thereafter brought near the positiondetecting device immediately, the voltage is insufficient to operate thepen control circuit 10 of the electronic pen.

In addition, in a case where an internal circuit other than the pencontrol circuit 10 is provided as a built-in circuit of the electronicpen, the internal circuit not being involved in signal transmission andreception by electromagnetic coupling to and from the position detectingdevice, and the internal circuit being, for example, a lighting circuitfor lighting an LED (Light Emitting Diode) or the like, the rectifiedoutput voltage in the capacitor 8 drops when the internal circuitoperates. Consequently, an original function of the electronic pen isaffected and becomes unstable.

In order to solve these problems, it is necessary to increase thecapacitance of the capacitor 8 in the rectifier circuit 5, andaccumulate an excess amount of energy effectively. However, increasingthe capacitance of the capacitor 8, in turn, slows the responsiveness ofthe electronic pen.

That is, with regard to the magnitude of the capacitance of thecapacitor 8, there is a problem of trade-off between improvement of theresponsiveness of the electronic pen and stable operation of theelectronic pen. Conventionally, there is no choice but to set thecapacitance of the capacitor 8 to a capacitance such that theresponsiveness and the stable operation are balanced as much aspossible. Therefore, with the circuit configuration of the conventionalelectronic pen of FIG. 7, it is difficult to be able to accumulate anexcess amount of resonance energy while maintaining a response speed ofthe electronic pen.

BRIEF SUMMARY

The present disclosure has been made in view of the above problems. Itis an object of the present disclosure to provide an electromagneticinduction type electronic pen that has a fast response speed and canperform stable operation by accumulating an excess amount of energyeffectively.

In order to solve the above problems, according to an embodiment of thedisclosure, there is provided an electronic pen including: a coil woundaround a magnetic core; a first capacitor forming a resonance circuitwith the coil; a rectifier circuit which, in operation, rectifies analternating-current signal received by the resonance circuit, therectifier circuit including a second capacitor; a voltage detectioncircuit which, in operation, detects whether a rectified output voltageobtained across the second capacitor of the rectifier circuit exceeds apredetermined value; a third capacitor having a capacitance that islarger than a capacitance of the second capacitor; and a charge controlcircuit which, in operation, detects supply of a charging current to thethird capacitor by the rectified output voltage; the charge controlcircuit, in operation, feeds the charging current to the third capacitorby the rectified output voltage when the voltage detection circuitdetects that the rectified output voltage across the second capacitorexceeds the predetermined value.

The electronic pen according to the embodiment of the disclosure has theabove-described constitution includes the third capacitor having acapacitance that is larger than the capacitance of the second capacitor,in addition to the second capacitor constituting a capacitor for storagein the rectifier circuit rectifying the alternating-current signalreceived by the resonance circuit constituted of the coil and the firstcapacitor.

The charge control circuit performs control such that the chargingcurrent flows to the third capacitor when the voltage detection circuitdetects that the rectified output voltage of the rectifier circuitexceeds the predetermined value. That is, when an excess amount ofenergy such as to cause the rectified output voltage of the rectifiercircuit to exceed the predetermined value is received through theresonance circuit, the charging current flows to the third capacitor,and the excess amount of energy is accumulated in the third capacitor.

Hence, the capacitance of the second capacitor in the rectifier circuitcan be set at a small value to increase the response speed of theelectronic pen in the operation of signal transmission and reception toand from the position detecting device by electromagnetic coupling, andeven when the energy received through the resonance circuit is reduced,the electronic pen can perform stable operation due to the voltagestored in the third capacitor. In addition, using the voltage stored inthe third capacitor as a power supply voltage for an internal circuit ofthe electronic pen can reduce an effect on the rectified output voltageobtained in the second capacitor in the rectifier circuit even when theinternal circuit consumes power.

Hence, the electronic pen according to the present disclosure can bothachieve a fast response speed and stable operation by accumulating anexcess amount of energy effectively.

According to the present disclosure, it is possible to provide anelectromagnetic induction type electronic pen that has a fast responsespeed and can perform stable operation by accumulating an excess amountof energy effectively.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an example configuration of an electroniccircuit in an electronic pen according to one or more embodiments of thepresent disclosure together with an example configuration of anelectronic circuit of a position detecting device;

FIG. 2 is a diagram showing an example mechanical configuration of anelectronic pen according to one or more embodiments of the presentdisclosure;

FIG. 3 is a diagram used to explain an example configuration of anelectronic circuit in an electronic pen according to one or moreembodiments of the present disclosure;

FIG. 4 is a diagram showing an example configuration of an electroniccircuit in an electronic pen according to one or more embodiments of thepresent disclosure;

FIG. 5 is a diagram showing another example configuration of anelectronic circuit in an electronic pen according to one or moreembodiments of the present disclosure;

FIG. 6 is a diagram showing a flowchart for explaining operation ofelectronic circuit shown in FIG. 5 according to one or more embodimentsof the present disclosure; and

FIG. 7 is a diagram showing an example configuration of an electroniccircuit in a conventional electronic pen.

DETAILED DESCRIPTION

An embodiment of an electronic pen according to the present disclosurewill hereinafter be described with reference to the drawings.

An example of a mechanical structure of the electronic pen according tothe embodiment will first be described with reference to FIG. 2.

A case (casing) 101 of the electronic pen 100 according to the presentembodiment has a bottomed cylindrical shape constituted of a first case102 and a second case 103 assembled and coupled to each other in anaxial direction. Formed on one end side in the axial direction of thefirst case 102 is an opening 102 a for projecting one end 109 a side ofa rod-shaped core body 109 to the outside, the one end 109 a sideconstituting a pen tip. A coil 104, a pen pressure detection circuit105, and a printed circuit board 107 mounted with electronic parts suchas a capacitor 106 forming a resonance circuit together with the coil104, a pen control circuit 110 formed by an IC, for example, arearranged in order in the axial direction and housed within a hollowportion of the case 101.

The coil 104 is wound around a ferrite core 108 as an example of acylindrical magnetic core, the ferrite core 108 having a through hole108 a in the axial direction. The core body 109 is configured not to bemechanically coupled to the ferrite core 108, and is disposed so as topass through the through hole 108 a of the ferrite core 108. The penpressure detection circuit 105 is housed on an opposite side of theferrite core 108 from the opening 102 a of the first case 102. Anotherend 109 b of the core body 109 is fitted into the pen pressure detectioncircuit 105. The core body 109 is moved and displaced in the axialdirection according to an applied pen pressure. The pen pressuredetection circuit 105 detects the movement and displacement of the corebody 109 as the pen pressure. The pen pressure detection circuit 105 inthe present example is configured to detect the pen pressure as a changein capacitance. The pen pressure detection circuit 105 can have theconstitution of a variable capacitance capacitor whose capacitancechanges according to the pen pressure, the variable capacitancecapacitor using a pen pressure detecting mechanism of a well-knownconstitution described in Patent Document: Japanese Patent Laid-Open No.2011-186803, for example. It is to be noted that the pen pressuredetection circuit 105 is not limited to this, but may have theconstitution of a variable capacitance capacitor using a semiconductorelement whose capacitance is variable according to the pen pressure, asdisclosed in Patent Document: Japanese Patent Laid-Open No. 2013-161307,for example. The pen pressure detection circuit 105 is electricallyconnected to the pen control circuit 110 on the printed board 107 by aterminal 105 a and a terminal 105 b.

The electronic pen 100 sends and receives electromagnetic waves to andfrom a position detecting device by a resonance circuit 111 constitutedof the coil 104 and the capacitor 106. The position detecting devicedetects a conductor sending and receiving electromagnetic waves to andfrom the electronic pen 100, and detects a position indicated by thecore body 109 of the electronic pen 100 as a coordinate position of theconductor.

8 Example of Circuit Configuration of Electronic Pen 100 and Example ofCircuit Configuration of Position Detecting Device 200

FIG. 1 is a diagram showing an example of an electronic circuit formedon the printed circuit board 107 of the electronic pen 100 according tothe present embodiment together with an example of circuit configurationof the position detecting device 200 that sends and receives signals byelectromagnetic induction coupling to the electronic pen 100.

The electronic pen 100 in the present embodiment is configured to sendand receive a signal for position detection by electromagnetic inductioncoupling to conductors of a sensor of the position detecting device 200,and transmit pen pressure information detected through the pen pressuredetection circuit 105 or the like to the position detecting device 200.

As described earlier, the electronic pen 100 has the parallel resonancecircuit 111 formed by connecting the capacitor 106 in parallel with thecoil 104 wound around the ferrite core 108. The capacitor 106constitutes a first capacitor. Further, as shown in FIG. 1, theelectronic pen 100 includes the pen control circuit 110 that controlsthe whole of the electronic circuit of the electronic pen 100, the pencontrol circuit 110 being formed by an IC in the present example.

An alternating-current signal received at the parallel resonance circuit111 from the position detecting device 200 by electromagnetic couplingis supplied through a capacitor 113 to a rectifier circuit 114constituted of diodes 115 and 116 and a capacitor 117 for storage of arectified voltage, is rectified by the rectifier circuit 114, and isstored in the capacitor 117. Then, the rectified output voltage obtainedacross the capacitor 117 is stabilized by a voltage stabilizationcircuit 122, and supplied as a power supply voltage for the pen controlcircuit 110. The capacitor 117 in the rectifier circuit 114 constitutesa second capacitor.

A switch circuit 112 is connected in parallel with the parallelresonance circuit 111 in the electronic pen 100 according to the presentembodiment. The switch circuit 112 is configured to be subjected toon-off control by the pen control circuit 110.

In addition, in the electronic pen 100 according to the presentembodiment, as shown in FIG. 1, a variable capacitance capacitor 105Cconstituting the pen pressure detection circuit 105 is connected to thepen control circuit 110. A resistance 123 is connected in parallel withthe variable capacitance capacitor 105C. In the present example, the pencontrol circuit 110 charges the variable capacitance capacitor 105C,thereafter makes the variable capacitance capacitor 105C dischargethrough the resistance 123, and measures a time taken for the voltage ofa terminal to which the variable capacitance capacitor 105C is connected(which voltage corresponds to a voltage across the variable capacitancecapacitor 105C) to reach a predetermined threshold value. The pencontrol circuit 110 thereby measures the capacitance of the variablecapacitance capacitor 105C.

The pen control circuit 110 detects a change in pen pressure from achange in the measured capacitance of the variable capacitance capacitor105C, and thus detects whether a pen pressure is applied to the corebody 109. In addition, when detecting that a pen pressure is applied,the pen control circuit 110 calculates the pen pressure value of the penpressure from the value of the capacitance of the variable capacitancecapacitor 105C.

In the present embodiment, as described earlier, the pen control circuit110 performs on-off control of the switch circuit 112 according toinformation about the calculated pen pressure value (pen pressure data).The pen control circuit 110 thereby transmits a digital signal of aplurality of bits corresponding to the pen pressure data as an ASKsignal or an OOK signal to the position detecting device 200.

The electronic pen 100 according to the present embodiment is furtherprovided with a voltage detection circuit 120 that detects whether ornot the rectified output voltage obtained across the storage capacitor117 in the rectifier circuit 114 is equal to or higher than apredetermined voltage set in advance. In addition, the electronic pen100 is provided with a series circuit of a charge control circuit 118and a capacitor 119 in parallel with the storage capacitor 117. Thecapacitor 119 constitutes a third capacitor. A capacitance C2 of thecapacitor 119 is larger than a capacitance C1 of the capacitor 117 inthe rectifier circuit 114, and is, for example, a few times to a few tentimes larger than the capacitance C1 of the capacitor 117. Incidentally,the capacitance C1 of the capacitor 117 in the rectifier circuit 114 isset at a relatively small value to be able to achieve a faster responsespeed at times of signal transmission and reception to and from theposition detecting device 200 by electromagnetic coupling.

The charge control circuit 118 in the example of FIG. 1 is formed by aswitch circuit, and is configured to be subjected to on-off controlaccording to a switching control signal from the voltage detectioncircuit 120. Specifically, when the rectified output voltage obtainedacross the capacitor 117 in the rectifier circuit 114 is not equal to orhigher than the predetermined voltage Eth set in advance, the voltagedetection circuit 120 controls the switch circuit constituting thecharge control circuit 118 in an off state by the switching controlsignal. When the rectified output voltage obtained across the capacitor117 in the rectifier circuit 114 becomes equal to or higher than thepredetermined voltage Eth set in advance, the voltage detection circuit120 controls the switch circuit constituting the charge control circuit118 in an on state by the switching control signal.

Here, the predetermined voltage Eth is a voltage value that makes thepen control circuit 110 operate stably when the voltage is stabilized bythe voltage stabilization circuit 122 and supplied as power supplyvoltage to the pen control circuit 110.

When the switch circuit constituting the charge control circuit 118 isturned on, the rectified output voltage obtained across the capacitor117 in the rectifier circuit 114 causes a charging current to flow tothe capacitor 119, so that the capacitor 119 is charged.

A voltage accumulated by charging the capacitor 119 is supplied to thevoltage stabilization circuit 122, and is supplied as power supplyvoltage to an internal circuit 121. The internal circuit 121 can beformed by a circuit unrelated to the operation of signal transmissionand reception to and from the position detecting device 200 through theresonance circuit 111 by electromagnetic coupling. For example, as willbe described later, the internal circuit 121 can be formed by a lightemission driving circuit driving a light emitting element such as an LEDor the like, a wireless communication circuit based on the Bluetooth(registered trademark) standard, or the like.

On the other hand, as shown in FIG. 1, the position detecting device 200has position detecting coils formed by stacking an X-axis direction loopcoil group 211X and a Y-axis direction loop coil group 212Y. The loopcoil groups 211X and 212Y are, for example, formed by n rectangular loopcoils and m rectangular loop coils, respectively. The loop coils formingthe respective loop coil groups 211X and 212Y are disposed so as to bearranged at equal intervals and sequentially overlap each other.

In addition, the position detecting device 200 has a selection circuit213 connected with the X-axis direction loop coil group 211X and theY-axis direction loop coil group 212Y. The selection circuit 213sequentially selects one loop coil of the two loop coil groups 211X and212Y.

The position detecting device 200 further includes an oscillator 221, acurrent driver 222, a switch connection circuit 223, a receptionamplifier 224, a detector 225, a low-pass filter 226, a sample and holdcircuit 227, an A/D (Analog to Digital) converter circuit 228, and acontrol circuit 229. The control circuit 229 is formed by amicrocomputer, for example.

The oscillator 221 generates an alternating-current signal of afrequency f0. The resonance frequency of the resonance circuit 111 inthe electronic pen 100 is selected such that the frequency f0 is acenter frequency. The alternating-current signal generated in theoscillator 221 is supplied to the current driver 222. The current driver222 converts the alternating-current signal supplied from the oscillator221 into a current, and sends out the current to the switch connectioncircuit 223. The switch connection circuit 223 selects a connectiondestination (a transmitting side terminal T or a receiving side terminalR) to which to connect the loop coil selected by the selection circuit213, under control of the control circuit 229. Of the connectiondestinations, the transmitting side terminal T is connected with thecurrent driver 222, and the receiving side terminal R is connected withthe reception amplifier 224.

An induced voltage generated in the loop coil selected by the selectioncircuit 213 is sent to the reception amplifier 224 via the selectioncircuit 213 and the switch connection circuit 223. The receptionamplifier 224 amplifies the induced voltage supplied from the loop coil,and sends out the amplified induced voltage to the detector 225.

The detector 225 detects the induced voltage generated in the loop coil,that is, a received signal, and sends out the received signal to thelow-pass filter 226. The low-pass filter 226 has a cutoff frequencysufficiently lower than the above-mentioned frequency f0. The low-passfilter 226 converts the output signal of the detector 225 into adirect-current signal, and sends out the direct-current signal to thesample and hold circuit 227. The sample and hold circuit 227 holds avoltage value of the output signal of the low-pass filter 226 inpredetermined timing, specifically, predetermined timing during areception period, and sends out the voltage value to the A/D convertercircuit 228. The A/D converter circuit 228 converts the analog output ofthe sample and hold circuit 227 into a digital signal, and outputs thedigital signal to the control circuit 229.

The control circuit 229 controls the selection of a loop coil in theselecting circuit 213, the switching of the switch connection circuit223, and the timing of the sample and hold circuit 227. The controlcircuit 229 makes an electromagnetic induction signal transmitted fromthe X-axis direction loop coil group 211X and the Y-axis direction loopcoil group 212Y for a certain transmission duration on the basis of theinput signal from the A/D converter circuit 228.

An electromagnetic induction signal transmitted from the electronic pen100 generates an induced voltage in each of the loop coils of the X-axisdirection loop coil group 211X and the Y-axis direction loop coil group212Y. The control circuit 229 calculates the coordinate values of anindicated position in an X-axis direction and a Y-axis direction whichposition is indicated by the electronic pen 100 on the basis of thelevel of the voltage value of the induced voltage generated in each loopcoil.

In addition, the control circuit 229 supplies the current driver 222with a signal for controlling interruption of a transmission signal anda signal for controlling the level of the transmission signal, andperforms processing of receiving additional information such as penpressure data, identification information, or the like from theelectronic pen 100. As will be described later, the control circuit 229detects an interrupted signal constituted by an ASK signal, for example,from the electronic pen 100 as a digital signal of a plurality of bits,and thereby detects the additional information such as the pen pressuredata, the identification information, or the like.

Operation of Electronic Pen 100 and Operation of Position DetectingDevice 200

The position detecting device 200 sends out a transmission signal on thebasis of processing control of the control circuit 229. Incidentally,the electronic pen 100 can also be electromagnetically coupled to adedicated charging device rather than the position detecting device 200,and thereby receive an alternating-current signal sent out from thededicated charging device.

When the electronic pen 100 is not in a state of receiving analternating-current signal from the position detecting device 200 or thecharging device by the parallel resonance circuit 111, the capacitor 117in the rectifier circuit 114 does not store electricity. The voltagedetection circuit 120 therefore does not detect a voltage equal to orhigher than the predetermined voltage Eth. Thus, the switch circuitconstituting the charge control circuit 118 is off, and the capacitor119 is not charged.

When the electronic pen 100 is then in a state of receiving analternating-current signal from the position detecting device 200 or thecharging device by the parallel resonance circuit 111, thealternating-current signal received by the parallel resonance circuit111 is rectified by the rectifier circuit 114, and is stored in thecapacitor 117. The capacitance C1 of the capacitor 117 in the rectifiercircuit 114 is small, as described earlier. Thus, a rectified outputvoltage VC1 obtained in the capacitor 117 in the rectifier circuit 114rises with a steep slope, as indicated by a solid line 301 in FIG. 3.

When the rectified output voltage VC1 obtained in the capacitor 117 inthe rectifier circuit 114 then exceeds the predetermined voltage Eth,the voltage detection circuit 120 detects that the rectified outputvoltage VC1 exceeds the predetermined voltage Eth, and turns on theswitch circuit constituting the charge control circuit 118. Thus, therectified output voltage VC1 obtained in the capacitor 117 in therectifier circuit 114 causes a charging current to start flowing to thecapacitor 119. The capacitance C2 of the capacitor 119 is a few times toa few ten times the capacitance C1 of the capacitor 117. Thus, a voltage(stored voltage) VC2 across the capacitor 119 rises gently, as indicatedby a solid line 302 in FIG. 3.

Meanwhile, at this time, while the alternating-current signal from theposition detecting device 200 or the charging device is obtained, therectified output voltage VC1 obtained in the capacitor 117 in therectifier circuit 114 rises. When the rectified output voltage VC1exceeds the predetermined voltage Eth, as indicated by the solid line301 in FIG. 3, the rectified output voltage VC1 changes from a steeprising slope to a slightly rising slope, due to the supply of thecharging current to the capacitor 119.

That is, when the rectified output voltage VC1 obtained in the capacitor117 in the rectifier circuit 114 is equal to or higher than thepredetermined voltage Eth, the pen control circuit 110 can operatestably on the power supply voltage from the voltage stabilizationcircuit 122. Hence, the rectified output voltage VC1 obtained in thecapacitor 117 in the rectifier circuit 114 does not need to be a highvoltage value equal to or higher than the predetermined voltage Eth, andthe charging current to the storage capacitor 117 after the rectifiedoutput voltage VC1 becomes equal to or higher than the predeterminedvoltage Eth represents an excess amount of energy.

In the electronic pen 100 according to the present embodiment, theexcess amount of energy causes a charging current to be supplied to thecapacitor 119, so that charging (storage) of the capacitor 119 isperformed. The charging (storage) of the capacitor 119 presents noproblem at all even when performed with a gentle slope, because thestable operating state of the pen control circuit 110 is maintained whenthe rectified output voltage VC1 obtained in the capacitor 117 in therectifier circuit 114 is equal to or higher than the predeterminedvoltage Eth.

Then, if the electronic pen 100 moves away from the position detectingdevice 200 or the charging device and consequently cannot obtain thereceived energy through the resonance circuit 111, in a case where thevoltage VC2 stored in the capacitor 119 has become equal to or higherthan the predetermined voltage Eth, the voltage VC2 stored in thecapacitor 119 provides a power supply voltage to the pen control circuit110 of the electronic pen 100 through the voltage stabilization circuit122. The pen control circuit 110 thus maintains the stable operatingstate. In this case, because of the large capacitance of the capacitor119, the pen control circuit 110 can continue the stable operating staterelatively long.

In addition, in the present embodiment, the electronic pen 100 isprovided with the internal circuit 121. However, even when the internalcircuit 121 is in an operating state, a power supply voltage for theinternal circuit 121 is supplied from the voltage VC2 stored in thecapacitor 119. Therefore, the rectified output voltage VC1 obtained inthe capacitor 117 in the rectifier circuit 114 is not decreased by theinternal circuit 121. Hence, the pen control circuit 110 of theelectronic pen 100 can operate stably.

In this case, when the switch circuit 112 of the electronic pen 100 isoff, the parallel resonance circuit 111 performs resonant operation onthe alternating-current signal transmitted from the position detectingdevice 200, and returns (feeds back) an electromagnetic induction signalto the position detecting device 200. The loop coils 211X and 212Y ofthe position detecting device 200 receive the electromagnetic inductionsignal from the resonance circuit 111 of the electronic pen 100. On theother hand, when the switch circuit 112 of the electronic pen 100 is on,the parallel resonance circuit 111 is prohibited from performing theresonant operation on the alternating-current signal from the positiondetecting device 200. Therefore, the electromagnetic induction signal isnot returned (fed back) from the parallel resonance circuit 111 to theposition detecting device 200, and the loop coils 211X and 212Y of theposition detecting device 200 do not receive the signal from theelectronic pen 100.

In the present example, during the position detecting operation ofdetecting a position indicated by the electronic pen 100, the controlcircuit 229 of the position detecting device 200 transmits analternating-current signal from the oscillator 221 to the electronic pen100 while sequentially selecting the loop coils 211X and the loop coils212Y, and switches to reception after the transmission and detects thelevel of the feedback signal. During the position detection, the pencontrol circuit 110 of the electronic pen 100 holds the switch circuit112 in an off state at all times, and is therefore always in a state offeeding back the alternating-current signal received by the parallelresonance circuit 111 to the position detecting device 200.

The control circuit 229 of the position detecting device 200 monitorsthe magnitude of the level of the feedback signal received by each ofthe loop coils 211X and the loop coils 212Y, and detects a coordinateposition indicated by the electronic pen 100 on the basis of the level.

Then, in the present example, the control circuit 229 of the positiondetecting device 200 detects the presence or absence of the receivedsignal from the electronic pen 100 a number of times which number isequal to the number of bits of information transmitted from theelectronic pen 100. The control circuit 229 thereby receives theinformation of a digital signal of the plurality of bits.

On the other hand, as described earlier, the pen control circuit 110 ofthe electronic pen 100 generates the digital signal of the plurality ofbits corresponding to the information such as pen pressure data or thelike to be transmitted to the position detecting device 200, and on thebasis of the digital signal of the plurality of bits, the pen controlcircuit 110 performs on-off control of the switch circuit 112 insynchronism with the transmission and reception of electromagneticinduction signals to and from the position detecting device 200.

The control circuit 229 of the position detecting device 200 can receivethe information as the digital signal from the electronic pen 100 bydetecting the presence or absence of the received signal from theelectronic pen 100 a number of times which number is equal to the numberof bits of the information transmitted from the electronic pen 100.

Effect of Embodiment

As described above, the electronic pen 100 according to theabove-described embodiment is provided with the capacitor 119 charged bythe rectified output voltage accumulated in the capacitor 117, inaddition to the capacitor 117 in the rectifier circuit 114. Theelectronic pen 100 according to the above-described embodiment performscontrol so as to supply a charging current to the capacitor 119 throughthe charge control circuit 118 when the voltage detection circuit 120detects that the voltage value of the rectified output voltageaccumulated in the capacitor 117 exceeds the predetermined voltage Eth.

Thus, according to the electronic pen 100 of the above-describedembodiment, it is possible to decrease the capacitance of the capacitor117 in the rectifier circuit 114 and thereby achieve a faster responsespeed at times of signal transmission and reception to and from theposition detecting device 200 by electromagnetic coupling, andaccumulate excess energy in the capacitor 119 having a largercapacitance than the capacitor 117. Then, the voltage accumulated in thecapacitor 119 can ensure a stable operation of the electronic pen 100,and a driving voltage for the internal circuit 121 can be supplied fromthe capacitor 119. The operation of the internal circuit 121 cantherefore be prevented from decreasing the rectified output voltage ofthe capacitor 117 in the rectifier circuit 114. It is thus possible tomaintain a stable operation of the electronic pen 100 with regard tosignal transmission and reception to and from the position detectingdevice 200 by electromagnetic coupling.

FIRST EXAMPLE Concrete Example of Charge Control Circuit 118 and VoltageDetection Circuit 120 and Concrete Example of Internal Circuit 121

Next, referring to FIG. 4, description will be made of an electronic pen100A according to a first example for explaining a concrete example ofcircuit configuration of the charge control circuit 118 and the voltagedetection circuit 120 of the electronic pen 100 described above and aconcrete example of configuration of the internal circuit 121 of theelectronic pen 100. Incidentally, the same parts as in the electronicpen 100 described above are identified by the same reference symbolsalso in the first example of FIG. 4, and repeated description thereofwill be omitted.

In the electronic pen 100A according to the first example of FIG. 4, thevoltage detection circuit 120 is formed by a Zener diode 133 whosebreakdown voltage (Zener voltage) is equal to or higher than thepredetermined voltage Eth. The charge control circuit 118 includes: aFET (Field Effect Transistor) 131 having a source-to-drain pathconnected in series with the Zener diode 133; and a FET 132 having agate commonly connected to the FET 131 and having a source-to-drain pathconnected in series with the capacitor 119.

In this case, a series circuit of the source-to-drain path of the FET131 and the Zener diode 133 is connected in parallel with the capacitor117 in the rectifier circuit 114. A series circuit of the capacitor 119and the source-to-drain path of the FET 132 is also connected inparallel with the capacitor 117 in the rectifier circuit 114.

A connection is established between the gate and source of the FET 131.The FET 131 is thereby diode-connected, so to speak, and is thusconfigured as a current source that feeds a predetermined current valueI. The diode-connected FET 131 and the FET 132 whose gate is commonlyconnected to the FET 131 constitute a current mirror circuit. The sizeof the FET 132 in the present example is n (n≧1) times that of the FET131, for example n=3 times that of the FET 131. When the Zener diode 133is turned on, and a current having a current value I flows through theFET 131 and the Zener diode 133, a charging current having a currentvalue 31 flows through the FET 132 to the capacitor 119.

In the present example, a point of connection between the capacitor 119and the source of the FET 132 is connected to the voltage stabilizationcircuit 122 through a diode 134.

In addition, the internal circuit 121 in the present example is a seriescircuit of an LED 135 as a light emitting element and a switch circuit136. That is, the point of connection between the capacitor 119 and thesource of the FET 132 is grounded through the series circuit of the LED135 and the switch circuit 136. The switch circuit 136 is to controlwhether or not to make the LED 135 emit light according to an operationof a user. A push-button switch 137 operated by the user is connected tothe pen control circuit 110.

Though not shown, an operating unit 137 a of the push-button switch 137is exposed from the case 101 shown in FIG. 2 to the outside, and isdisposed so as to be operable by the user. In addition, the LED 135 is,for example, disposed in the vicinity of the pen tip side within thecase 101 shown in FIG. 2, and at least a part of the case 101 on the pentip side in the vicinity of a position in which the LED 135 is disposedis a transparent part so that light emitted by the LED 135 brightlyilluminates the vicinity of a position indicated by the pen tip side(one end 109 a side of the core body 109) of the electronic pen 100A.

Further, in the first example, information transmitted from theelectronic pen 100A to the position detecting device 200 includes notonly pen pressure data but also identification information (ID)including a manufacturer number and a product number of the electronicpen 100A. Therefore, as shown in FIG. 4, the pen control circuit 110 isconnected with an ID memory 138 that stores the identificationinformation (ID) including the manufacturer number and the productnumber of the electronic pen 100A.

The pen control circuit 110 detects a pen pressure from the capacitanceof the variable capacitance capacitor 105C formed by the pen pressuredetection circuit 105 and generates pen pressure data, as describedearlier, further reads the identification information from the ID memory138, and generates a digital signal constituted of the generated penpressure data and the read identification information. Then, the pencontrol circuit 110 transmits the digital signal to the positiondetecting device 200 by controlling the switch circuit 112.

In the present example, when the user desires to make the LED 135 emitlight, the user provides input to that effect to the pen control circuit110 in advance by pressing the operating unit 137 a of the push-buttonswitch 137. When the electronic pen 100A receives an alternating-currentsignal from the position detecting device 200 or the charging device inthis state and charges the capacitor 117 in the rectifier circuit 114,and then the rectified output voltage exceeds the predetermined voltageEth, the pen control circuit 110 is set in an operating state. Then, thepen control circuit 110 starts control for signal transmission andreception to and from the above-described position detecting device 200by electromagnetic coupling, and detects the state of operation of thepush-button switch 137 and turns on the switch circuit 136 when thepush-button switch 137 is set in a state that makes the LED 135 emitlight.

Then, in the electronic pen 100A in the present example, when thecapacitor 117 in the rectifier circuit 114 is charged and the rectifiedoutput voltage exceeds the predetermined voltage Eth, the Zener diode133 causes breakdown and is thereby turned on, so that a current havingthe current value I flows through the FET 131 and the Zener diode 133.Then, a charging current having the current value 31 flows through thecurrent-mirror-connected FET 132 to charge the capacitor 119.

When a voltage stored in the capacitor 119 then rises to such a voltageas to be able to make the LED 135 emit light, and when the switchcircuit 136 is on, a driving current flows through the LED 135, so thatthe LED 135 emits light. The light emission of the LED 135 brightlyilluminates the pen tip side, which is the one end 109 a side of thecore body 109 of the electronic pen 100A in the present example. Thelight emission of the LED 135 also enables the user to recognize thatthe voltage stored in the capacitor 119 has become equal to or higherthan a predetermined value that makes the internal circuit 121 operableand that the electronic pen 100A is set in a stable operating state.

The electronic pen 100A according to the first example described abovecan light the LED 135 without interfering with the original operationalfunction as an electronic pen even though the electronic pen 100A doesnot have a battery. Moreover, with regard to the original operationalfunction as an electronic pen, an effect of being able to achieve afaster response speed is produced.

Incidentally, in the above-described first example, the arrangementposition of the LED 135 is in the vicinity of the pen tip side of theelectronic pen 100A. However, the arrangement position of the LED 135 isnot limited to this, but may be an arbitrary position such as in an endportion on the opposite side from the pen tip side of the case 101 ofthe electronic pen 100A, a central portion in the axial direction of thecase 101, or the like. However, it is needless to say that in eithercase, the vicinity of the arrangement position of the LED 135 in thecase 101 is formed such that the light emitting state of the LED 135 isvisible from the outside.

SECOND EXAMPLE Concrete Example of Charge Control Circuit 118 andVoltage Detection Circuit 120 and Concrete Example of Internal Circuit121

Next, referring to FIG. 5, description will be made of an electronic pen100B according to a second example as another example of a concreteexample of the charge control circuit 118 and the voltage detectioncircuit 120 and a concrete example of the internal circuit 121. In thesecond example of FIG. 5, the same parts as in the first example of FIG.4 are identified by the same reference symbols, and repeated descriptionthereof will be omitted.

The electronic pen 100B in the second example of FIG. 5 is differentfrom the electronic pen 100A in the first example of FIG. 4 in that theelectronic pen 100B has a different configuration in the internalcircuit 121 and is not provided with the push-button switch 137.

Specifically, an internal circuit 121B of the electronic pen 100Baccording to the second example includes a communication circuit 141, anauthentication circuit 142, an LED 143, and a switch circuit 144. Thecommunication circuit 141 in the present example has a configuration ofa wireless communication circuit based on the Bluetooth (registeredtrademark) standard, and is driven by using a voltage stored in thecapacitor 119 as a driving voltage. Incidentally, a position detectingdevice used in conjunction with the electronic pen 100B according to thepresent second example is provided with communication circuit thatperforms wireless communication with the communication circuit 141 ofthe electronic pen 100B.

The authentication circuit 142 is driven by also using the voltagestored in the capacitor 119 as a power supply voltage. Thisauthentication circuit 142 is connected to the communication circuit141. The authentication circuit 142 sends first authenticationinformation for making the position detecting device authenticate theelectronic pen 100B to the position detecting device through thecommunication circuit 141, and receives, through the communicationcircuit 141, second authentication information for authenticating theposition detecting device which second authentication information istransmitted from the position detecting device and then authenticatesthe position detecting device on the basis of the second authenticationinformation. The first authentication information and the secondauthentication information are encrypted to enhance security. Theauthentication circuit 142 performs decryption processing correspondingto the encryption. Therefore, the authentication circuit 142 is notconfigured as a function of the pen control circuit 110, but isconfigured as a separate circuit.

The authentication circuit 142 transmits a result of the authenticationto the position detecting device through the communicating circuit.Incidentally, identification information of the electronic pen 100B readfrom the ID memory 138 is added to the first authentication informationtransmitted from the electronic pen 100B to the position detectingdevice.

The position detecting device also includes an authentication circuit inaddition to the communication circuit. The position detecting deviceauthenticates the electronic pen 100B on the basis of the firstauthentication information from the electronic pen 100B. The positiondetecting device then transmits a result of the authentication to theelectronic pen 100B.

As described above, each of the electronic pen 100B and the positiondetecting device mutually authenticates the other, and mutually sends aresult of the authentication to the other. The electronic pen 100B andthe position detecting device then determine that authentication isachieved when confirming that the mutual authentication is achieved.When the authentication is achieved, the electronic pen 100B becomesable to perform indication input to the position detecting device, andthe position detecting device detects a position indicated by theelectronic pen 100B whose authentication is confirmed, while monitoringthe identification information sent from the electronic pen 100B. Whenthe authentication circuit 142 of the electronic pen 100B confirms theabove-described mutual authentication between the electronic pen 100Band the position detecting device, the authentication circuit 142notifies the pen control circuit 110 to that effect.

Further, in the electronic pen 100B according to the present secondexample, the point of connection between the capacitor 119 and thesource of the FET 132 is grounded through a series circuit of the LED143 and the switch circuit 144. The switch circuit 144 is off in aninitial state (normal state). The switch circuit 144 is controlled to beswitched on by a switching control signal from the pen control circuit110. When the pen control circuit 110 receives a notification from theauthentication circuit 142 to the effect that the above-described mutualauthentication between the electronic pen 100B and the positiondetecting device is confirmed, the pen control circuit 110 performscontrol so as to turn on the switch circuit 144. Hence, the LED 143illuminates and emits light only when the mutual authentication betweenthe electronic pen 100B and the position detecting device is confirmed.A user can recognize on the basis of the illumination and the lightemission of the LED 143 that the mutual authentication between theelectronic pen 100B and the position detecting device is confirmed.

The other configuration of the electronic pen 100B is similar to that ofthe electronic pen 100A.

Operation of the electronic pen 100B at a time of mutual authenticationbetween the electronic pen 100B and the position detecting device willbe described with reference to a flowchart of FIG. 6. Incidentally, theprocessing of each step in the flowchart of FIG. 6 is performed mainlyby the pen control circuit 110 except authentication processing. Theauthentication processing is performed by the dedicated authenticationcircuit 142.

When the electronic pen 100B receives an alternating-current signal fromthe position detecting device or a charging device and charges thestorage capacitor 117 in the rectifier circuit 114, and then therectified output voltage exceeds the predetermined voltage Eth, the pencontrol circuit 110 is set in an operating state. Then, the pen controlcircuit 110 starts the processing shown in the flowchart of FIG. 6, anddetermines whether or not communication with the position detectingdevice is possible by checking states of operation of the communicationcircuit 141 and the authentication circuit 142 (S101).

Also in the electronic pen 100B in the present example, when thecapacitor 117 in the rectifier circuit 114 is charged and the rectifiedoutput voltage exceeds the predetermined voltage Eth, the Zener diode133 causes breakdown and is thereby turned on, so that a current havingthe current value I flows through the FET 131 and the Zener diode 133.Accordingly, a charging current having the current value 31 flowsthrough the FET 132 to charge the capacitor 119. While the voltagestored in the capacitor 119 does not rise to an operating voltage of thecommunication circuit 141 and the authentication circuit 142,communication between the electronic pen 100B and the position detectingdevice is not possible at S101. The pen control circuit 110 thereforecontinues to S101. At this time, the switch circuit 144 remains off.

When the voltage stored in the capacitor 119 then rises to become equalto or higher than the operating voltage of the communication circuit 141and the authentication circuit 142, the pen control circuit 110determines at S101 that communication between the electronic pen 100Band the position detecting device is possible. Then, the pen controlcircuit 110 blinks the LED 143 by repeatedly turning the switch circuit144 on and off in predetermined cycles (S102). At this time, thecommunication circuit 141 and the authentication circuit 142 are set inan operating state, and therefore the above-described mutualauthentication processing is performed (S103). Hence, the blinking ofthe LED 143 notifies the user that the electronic pen 100B is performingoperation for the mutual authentication processing between theelectronic pen 100B and the position detecting device.

Next, the pen control circuit 110 determines whether or not anotification to the effect that mutual authentication is confirmed isreceived from the authentication circuit 142 (S104). When determiningthat the notification is not received, the pen control circuit 110returns the processing to S101 to repeat the processing from S101 ondown.

When the pen control circuit 110 determines that the notification to theeffect that mutual authentication is confirmed is received from theauthentication circuit 142, the pen control circuit 110 switches on theswitch circuit 144 to make the LED 143 illuminate and emit light (S105).The user recognizes on the basis of the illumination and the lightemission of the LED 143 that mutual authentication with the positiondetecting device is achieved.

Next, the pen control circuit 110 starts operation as theabove-described electronic pen with the authenticated position detectingdevice (S106). Specifically, by receiving an electromagnetic wave fromthe position detecting device by the resonance circuit 111 and feedingback the electromagnetic wave through the resonance circuit 111, theelectronic pen 100B transmits a signal for position detection to theposition detecting device, and transmits pen pressure data and theidentification information as a digital signal. Incidentally, the penpressure data and the identification information may be transmitted tothe position detecting device through the communication circuit 141.

Next, the pen control circuit 110 determines whether or not thecommunication with the position detecting device has become impossible(S107). When determining that the communication has not becomeimpossible, the pen control circuit 110 continues the processingoperation as the electronic pen. When determining that the communicationhas become impossible, the pen control circuit 110 returns theprocessing to S101 to repeat the processing from S101 on down.

According to the electronic pen 100B in the second example describedabove, the communication circuit 141 and the authentication circuit 142for performing mutual authentication with the position detecting deviceare configured to operate on the voltage stored in the capacitor 119.Thus, processing operation for the mutual authentication does not affectthe voltage stored in the storage capacitor 117 in the rectifier circuit114 that supplies a driving voltage to the pen control circuit 110. Theelectronic pen 100B can therefore stably perform operation as anelectronic pen by electromagnetic coupling to the position detectingdevice even during the mutual authentication processing operation.

Other Embodiments or Modifications

It is needless to say that the internal circuit 121 of the electronicpen is not limited to the above-described examples. For example, theinternal circuit may be formed by a wireless communication circuit basedon the Bluetooth (registered trademark) standard, and the wirelesscommunication circuit may transmit the identification information of theelectronic pen and pen pressure data to the position detecting device.

In addition, second authentication information may be set in theelectronic pen 100B, and the electronic pen 100B may perform a procedurefor authentication with the position detecting device by receiving firstauthentication information for authentication with the electronic pen100B, the first authentication information being transmitted from theposition detecting device to the electronic pen 100B through thecommunication circuit 141.

While a preferred embodiment of the present disclosure has beendescribed using specific terms, such description is for illustrativepurposes only, and it is to be understood that changes and variationsmay be made without departing from the spirit or scope of the followingclaims.

What is claimed is:
 1. An electronic pen comprising: a coil wound arounda magnetic core; a first capacitor forming a resonance circuit with thecoil; a rectifier circuit which, in operation, rectifies analternating-current signal received by the resonance circuit, therectifier circuit including a second capacitor; a voltage detectioncircuit which, in operation, detects whether a rectified output voltageacross the second capacitor of the rectifier circuit exceeds apredetermined value; a third capacitor having a capacitance that islarger than a capacitance of the second capacitor; and a charge controlcircuit which, in operation, controls supply of a charging current tothe third capacitor by the rectified output voltage; wherein the chargecontrol circuit, in operation, causes the charging current to be fed tothe third capacitor by the rectified output voltage when the voltagedetection circuit detects that the rectified output voltage across thesecond capacitor exceeds the predetermined value.
 2. The electronic penaccording to claim 1, wherein the capacitance of the third capacitor istwo or more times the capacitance of the second capacitor.
 3. Theelectronic pen according to claim 1, further comprising: a first circuitwhich, in operation, operates on the rectified output voltage of therectifier circuit; and a second circuit which, in operation, operates ona charge voltage of the third capacitor.
 4. The electronic pen accordingto claim 3, wherein the first circuit, in operation, controls processingin the electronic pen.
 5. The electronic pen according to claim 4,wherein: the resonance circuit is electromagnetically coupled to aposition detecting sensor, and the first circuit, in operation, controlsa signal transmitted to the position detecting sensor through theresonance circuit.
 6. The electronic pen according to claim 3, wherein:the resonance circuit is electromagnetically coupled to a positiondetecting sensor, and the second circuit, in operation, completesprocessing within the electronic pen irrespective of signal transmissionand reception of the resonance circuit to and from the positiondetecting sensor by electromagnetic coupling.
 7. The electronic penaccording to claim 3, further comprising: a light emitter which, inoperation, emits light visibly to an outside of a casing, wherein thesecond circuit includes a light emission driver circuit which, inoperation, drives the light emitter.
 8. The electronic pen according toclaim 7, further comprising: an operating element which, in operation,is operated by a user; and a light emission control circuit which, inoperation, controls light emission by the light emitter according to anoperation of the operating element.
 9. The electronic pen according toclaim 3, wherein the second circuit includes a wireless communicationcircuit which, in operation, wirelessly communicates information. 10.The electronic pen according to claim 3, wherein the second circuitincludes an authentication circuit which, in operations, performs mutualauthentication with a position detecting device.
 11. The electronic penaccording to claim 3, wherein the predetermined value used by thevoltage detection circuit in detecting whether the rectified outputvoltage exceeds the predetermined value is equal to or higher than anoperating voltage of the first circuit.
 12. A method comprising:providing an electronic pen with a resonance circuit that includes afirst capacitor and a coil wound around a magnetic core; rectifying analternating-current signal received by the resonance circuit using arectifier circuit that includes a second capacitor; detecting whether arectified output voltage across the second capacitor exceeds apredetermined value; controlling supply of a charging current to a thirdcapacitor by the rectified output voltage, the third capacitor having acapacitance that is larger than a capacitance of the second capacitor ofthe rectifier circuit; and feeding the charging current to the thirdcapacitor by the rectified output voltage when the detecting detectsthat the rectified output voltage across the second capacitor exceedsthe predetermined value, based on the controlling.
 13. The methodaccording to claim 12, further comprising: operating a first circuitusing the rectified output voltage of the rectifier circuit; andoperating a second circuit using a charge voltage of the thirdcapacitor.
 14. The method according to claim 13, further comprising:electromagnetically coupling the resonance circuit to a positiondetecting sensor, and controlling, by the first circuit, a signaltransmitted to the position detecting sensor through the resonancecircuit.
 15. The method according to claim 13, further comprising:electromagnetically coupling the resonance circuit to a positiondetecting sensor, and completing processing within the electronic penirrespective of signal transmission and reception of the resonancecircuit to and from the position detecting sensor by electromagneticcoupling.
 16. The method according to claim 13, further comprising:controlling, by the second circuit, emission of light from a lightemitter to an outside of a casing.
 17. The method according to claim 16,wherein the controlling, by the second circuit, of the emission of lightfrom the light emitter is based on a user operation of an operatingelement.
 18. The method according to claim 13, further comprising:wirelessly communicating information using the second circuit.
 19. Themethod according to claim 13, further comprising: performing mutualauthentication with a position detecting device using the secondcircuit.
 20. The method according to claim 13, wherein the predeterminedvalue is greater than or equal to an operating voltage of the firstcircuit.